The intake of internal combustion engines is formed from multiple pieces that are coupled together, some via welding, and some via fasteners. The fastened joints are provided to aid in assembly of the engine system and for serviceability.
Fasteners are provided to couple a joint 10, which in the example in FIG. 1 is an electronic throttle body (ETB) 12 to an intake manifold 32. Only a portion of ETB 12 and only a small portion of intake manifold 32 are shown in an exploded view in FIG. 1 of assembly 10. ETB 12 has an opening 14 that fluidly couples with opening 44 in intake manifold 32 when assembled. Three to four fasteners 22 (only 2 are shown in the cross-sectional view in FIG. 1) pass through holes 16 in ETB 12 and into threaded holes 36. Holes 16 are provided in tabs 18 that extend outwardly from the duct portion of ETB 12. ETB 12 has a circular groove 20 into which a gasket 24 is situated. When, gasket 24 is crushed by pulling ETB 12 against intake manifold 32 via fasteners 22, gasket 24 seals joint 10.
Intake manifold 32 has tabs 34 in which an insert 38 is provided that has internal threads 36 that mate with threads of fastener 22. Insert 38 has a stake 40 to prevent rotation of insert 38. Alternatively, insert 38 has a knurled or grooved outer surface to prevent rotation.
ETB 12 is made of metal and intake manifold 32 is commonly injection-molded plastic with fasteners 22 and inserts 38 being made out of a metal. Inserts 38 can be installed in intake manifold 32 by overmolding or by heating up the insert and then forcing them into holes in tabs 34 where they melt the adjacent plastic. When the plastic cools, insert 38 is captured. Either assembly technique introduces extra steps and complication and cost. And, with fastener 22 and inserts 38 being made of metal, they add more weight than the parent plastic parts.
In an effort to simplify, an alternative approach for a joint 50 in which an ETB 12 is coupled with an intake manifold 52 is shown in FIG. 2. Intake manifold, with an internal duct 54 has tabs 58 that extend outwardly. As manufactured, threaded holes 56 in tabs 58 do not exist. Threaded fasteners 26 are self tapping and form threaded holes 56 during assembly. It has been found, though, that in testing such a configuration that the threads in threaded holes 56 creep over time while the threads of metallic fastener 26 do not creep in such a way. At some point when the creep is substantial, clamping load provided by the coupling of fasteners 26 with threaded holes 56 reduces to zero. Through holes 16 in ETB 12 are provided with some additional clearance to allow proper assembly in light of manufacturing tolerance. With a nonzero clamping load, ETB 14 and intake manifold 52 are prevented from moving with respect to each other. However, when the clamping load goes to zero, the two move side-to-side, as shown by arrow 55, with respect to each other. This causes fretting of Gasket 24 and failure of joint 50 leading to leaking.
An assembly configuration in which inserts 38 are obviated that has a long service life is desired.